Effect of T H E Virus : Host Cell Relationship on Infection W Ith Vaccinia

In the course of certain recent experiments (1) it was observed that the chance of a virus preparation causing infection in an animal could not be predicted solely by the amount of virus injected and by the host's resistance but was influenced by still another variable. I t seemed possible that this variable might be the tissue mass (number of cells) exposed to each virus particle. If this were true it would be a new aspect of the well recognized obligate parasitism of viruses and would be also of practical importance in experiments concerned with titration of viruses in animals. In order to examine this possibility experiments were designed in which the amount of virus and the host resistance were kept constant but the number of host cells exposed to the virus varied. This was done by three types of experiments: (1) varying the amount of inoculum, (2) localizing and (3) increasing the spread of a constant quantity of virus. Localization was accomplished by injecting the animals with estrogenic hormone which Sprunt and McDearman (2) had shown to localize the spread of particulate material. Increase in spread was accomplished by adding an aqueous extract of testis to the virus preparation following the work of Duran-Reynals (3). These experiments all showed that the tissue mass (number of cells) exposed to the virus was an important factor in predicting the chance of a lesion.